JPS5897676A - Neutron detector - Google Patents

Abstract

PURPOSE:To measure only neutrons accurately and to permit measurement of neutrons in a wide range by putting a detector in a vacuum vessel and using glass for the main material of microchannel plates. CONSTITUTION:A reactive material 2 which release alpha particles of high velocities by reacting with neutrons is formed like a thin film at roughly the center in a vacuum vessel 1, and microchannel plates 3 wherein many glass tubes are bundled and formed like plates are installed on both sides thereof in tight contact therewith. Conductive anodes 4 for collecting electrons amplified by the plates 3 are installed in parallel on the outer sides thereof and the two anodes 4 are connected electrically by means of a conductive cable 5. The output of the neutron detector is run via a terminal 9 to a load resistor 11, and the pulselike voltages generated by the same are inputted as output signals to an output processing circuit consisting of a preamplifier 12, a main amplifier 13, a discriminator 14 and a counter circuit 15.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for quantitatively detecting neutrons (in particular, an apparatus that has almost no sensitivity to X-rays and γ-rays and is capable of measuring neutron doses over a wide range).

From the high-temperature plasma of the fusion device, snow H+ "H→("H@ +0.82 M*V )+ is produced by the following nuclear fusion reaction.
(n + 2.45 M@V)tH+easyH−+ (
'He +3.52 M@V )+ (n + 1
4.06 M@V ) neutrons (,) are generated, but at the same time γ-rays and hard X-rays (I M@V ~20
0 K@V ) X-rays due to bremsstrahlung radiation (200 K@V
X-rays such as ~10 K@V) are emitted. Conventionally, when measuring neutrons with a high background of X-rays and r-rays, RH-Kakunta and BF3-Kakunta are used, but these 1H-Kakunta, IIF, and Kakunta are not suitable for r-rays and X-rays. Because it is sensitive to radiation, it was necessary to shield the area around the detection device with lead to block X-rays and r-rays. However, in this case, since neutrons are also scattered by the lead, there is a drawback that the measurement accuracy of the absolute amount of neutrons becomes extremely poor when the amount of neutrons generated is small.

On the other hand, when the neutron dose becomes high, such as 10' eps or more, the 3He counter, BP, and Kakunta have the disadvantage that they cannot be measured due to their slow response speeds.

The present invention has been made to eliminate such drawbacks, and uses a reactant that reacts with neutrons to release α particles in a vacuum container and α particles placed outside the reactant to generate secondary electrons. The neutron detector is composed of a neutron detector equipped with an amplifying mechanism and an anode for collecting the amplified electron flow, and an output processing circuit that processes the electrical signal output from the neutron detector. The secondary electron amplification mechanism consists of a microchannel plate formed by a number of thin glass tubes whose inner walls are coated with a secondary electron emitting material. In an X-ray atmosphere, the amount of neutron generation changes rapidly over time, and the amount of change is 104
It is an object of the present invention to provide a neutron detection device that can accurately measure only neutrons even in cases where the number of neutrons reaches up to 101.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, the neutron detector is housed in a vacuum container 1, which is made of a material such as stainless steel, glass, or aluminum, and is equipped with a vacuum pump (not shown) such as a turbo molecular pump or an ion pump. After being evacuated to a high vacuum state by a method, it is sealed by any suitable method known in the art.

A reactant material 2, which reacts with neutrons and releases high-speed α particles, such as -Li or 1°B, is arranged in a thin film form approximately in the center of the vacuum container 1, and on both sides thereof, a reactant material 2 with an inner diameter of 10 to
Microchannel plates 3 and 6, which are formed by bundling a large number of 25 μm thin glass tubes and forming a plate shape with a thickness of about 0.5 to 1 m, are placed in close contact with each other. The inner wall of each glass tube of this microchannel plate 3 is coated with a secondary electron emitting material having an appropriate resistance value, so that each glass tube forms an independent continuous secondary electron amplifier. It has become. . Conductive anodes 4.4 are installed in parallel on the outside of the microchannel plates 3, 3 to collect electrons amplified by the plates 3, and the two anodes 4, 4 are connected to each other by conductive cables 5. electrically connected. Further, a high voltage is applied to the microchannel plate 3 from outside the vacuum vessel 1 via a terminal 6°7 between the reactant 2 side and the anode 4 side by a high voltage power supply 8 so that the reactant 2 side is negative.
Furthermore, a low voltage is applied between the outlet end of the plate 6 and the anode 4 from outside the vacuum vessel 1 via a terminal 7.9 by a low voltage power source 10 so that the plate 6 becomes negative.

The output of such a neutron detector is passed through a terminal 9 to a load resistor 11, and the resulting pulsed voltage is sent to a preamplifier 12, a main amplifier 13, a discriminator 14, and a counter circuit as an output signal. 15, or an output processing circuit as shown in FIG.

The output processing circuit shown in FIG. 2 is configured to be able to measure a wide range of neutron doses, from extremely low to high. Low neutron dose circuit system or integrator 2 consisting of a discriminator 18 and a counting circuit 19
0 and an ammeter 21 in the high neutron dose circuit system. Each of these circuit systems is provided with a feedback loop 22, 25 that switches the signal distributor 17 when the count value and current value reach certain values.

Next, the operation of the neutron detection device configured as above will be explained.

As shown in FIG. 6, when a neutron 24 is incident on a reactant 2 such as .Li or 1.l from outside the vacuum container 1, the following nuclear reaction -Li + n-'He +"H" B + n- 1 → 4He +7L1 releases high-speed helium (α particles) 25. These particles 25 enter the glass tube of the microchannel plate B, hit the inner wall, and emit secondary electrons. When a high voltage is applied to both ends of this glass tube by a high voltage power supply 8, an axial electric field is generated inside the glass tube, and the secondary electrons emitted from the inner wall of the glass tube are accelerated by this electric field and the relationship between their initial velocity and It draws a parabola and collides with the opposing surface, emitting new secondary electrons. This is repeated many times from the entrance to the exit of the glass tube, and as a result, the electron flow increases exponentially. This electron flow is collected at the anode 4 and the load resistance 1
1. Since this electron current flows in a pulse-like manner of several nanometers, a pulse-like voltage is generated across the load resistor 11.

This voltage signal is several mV when the load resistance 11 is 500.
This is pulse-amplified in the preamplifier 12, further amplified to 0.1 to several V in the main amplifier 16, and then the discriminator 14 discriminates the noise component and the pulse signal component. The pulse signal is shaped and input to the counting circuit 15. The number of pulses (-p-) counted by the counting circuit 15 is proportional to the number of incident neutrons.

However, when the number of incident neutrons ranges over a wide range from a few ep- to more than 10 maap1, it is convenient to use an output processing circuit as shown in FIG. That is,
When the output pulse of the neutron detector is input to this output processing circuit, it is amplified by the broadband DC amplifier 16 and then input to either the low neutron dose circuit system or the high neutron dose circuit system by the signal distributor 17. be done. Now, when input to the low neutron dose circuit system, the high-speed discriminator 1
At step 8, a pulse signal is distinguished from noise, and the pulse is shaped and input to the counting circuit 19. The count value of this counting circuit 19 is proportional to the neutron dose, but when the count value is 10' cps
If the temperature exceeds that level, the circuit system will suffocate and become unresponsive.
Feedback loop 22 provides a trigger signal to signal distributor 17 to switch the circuit for high neutron doses. In this circuit system, an input signal is integrated by an integrator 20 and measured in an analog manner by an ammeter 21.

However, when the input signal changes during measurement and the analog measurement has a lot of noise, that is, when the ammeter 21
When the current value falls below a certain value, the feedback loop 23 provides a trigger signal to the signal distributor 17 and the circuit is switched for low neutron doses.

As is clear from the above explanation, in the neutron detection device of the present invention, since the detector is located in a vacuum and the main material of the microchannel plate is glass, there is almost no interaction with X-rays or R-rays. , low doses of neutrons can be measured even when the background of X-rays and r-rays is high. Furthermore, since the device of the present invention can measure neutrons in a wide range from a low neutron dose of a few epH to a very high neutron dose, the amount of neutron generation changes rapidly over time, and the amount of change changes nearly 104 to 101. Accurate measurements can be made in any case. Furthermore, since the device of the present invention is small and extremely thin, it can perform measurements even if there are space constraints.

[Brief explanation of drawings]

FIG. 1 is a configuration circuit diagram showing an embodiment of the neutron detection device of the present invention, FIG. 2 is a block diagram showing a modified example of the output processing circuit of the neutron detection device of the present invention, and FIG. It is an explanatory diagram showing the action of a detector. 1 ...... Vacuum container 2 ...... Reactant 6 ...... Microchannel plate 4 ...... Anode 12 ・...... Preamplifier 13 ...
... Main amplifier 14.18... Discriminator 15.19...
・ Counting circuit 16 ...... DC amplifier 17 ...
・・・・・・ Signal distributor 20 ・・・・・・・・・
Integrator 21 ・・・・・・ Current needle 22.25... Fitno (tsukup 24 ・
・・・・・・・・・ Neutron 25 ・・・・・・・・・ Alpha particle agent Patent attorney Sa Suyama - Figure 1

Claims (1)

[Claims] 1. Inside the vacuum container ζ2, a reactant that reacts with neutrons and releases α particles, a mechanism that generates secondary electrons and amplifies them by the α particles placed outside the reactant, and this mechanism. It consists of a neutron detector equipped with an anode for collecting the amplified electron flow, and an output processing circuit that processes the electrical signal output from the neutron detector, and is configured to amplify the secondary electrons. A neutron detection device characterized in that the mechanism consists of a microchannel plate formed by a number of thin glass tubes whose inner walls are coated with a secondary electron emitting material. 2. The neutron detection device according to claim 1, wherein the reactant is composed of 'Li or 1.B, and is arranged in the form of a thin film in the center of the vacuum vessel. 3. The output processing circuit includes a DC amplifier that amplifies the output signal from the neutron detector, a signal distributor that distributes the signal according to the neutron dose, and a signal distributor connected to the signal distributor that converts the input signal into a noise component. A low neutron dose circuit system consisting of a discriminator that discriminates into pulse signal components and pulse shaping and a counting circuit that counts the number of pulses, and a high neutron dose circuit system consisting of an integrator and a current needle that integrates the input signal. A neutron detection device according to claim 1, comprising: